Method of making molten metal for casting

ABSTRACT

A method for making molten metal for casting directly from cold starting material. Cold starting material is placed in a movable vessel, and a layer of particulate material selected from the group consisting of coke and flux is spread on the top of the starting material in the vessel. One or more flames of hydrocarbon fuel-oxygen mixture are directed to the particulate layer, while translating the vessel along a closed path, so as to heat the particulate to white-hot state and to mix the cold starting material with the particulate thus heated, for melting the starting material. A composition-control agent is added in the material thus melted for producing desired composition of molten metal, while maintaining the flames and the translation. A fluid curtain is formed around the flames to inhibit the flames from directly burning the inner surface of the vessel.

llited States Patent [151 3,653,877

Enya [451 Apr. 4, 1972 54] METHOD OF MAKING MOLTEN 3,360,253 12/1967Mori et a1. ..266/39 x METAL FOR CASTING Ryosuke Enya, No. 3620Shinichi, Murozumi-cho, Hikari,Japan Mar. 6, 1970 Inventor:

Filed:

Appl. No.:

Field of Search ..75/40, 43, 45, 46, 61, 65; 266/35, 39, 34 R ReferencesCited UNITED STATES PATENTS 7/l96l Trentini et al. ..266/35 X 5/1967Rinesch ..75/6l X 3,540,712 11/1970 Hohle ..266/36 P PrimaryExaminer-Henry W. Tarring, ll Attorney-Young & Thompson [57] ABSTRACT Amethod for making molten metal for casting directly from cold startingmaterial. Cold starting material is placed in a movable vessel, and alayer of particulate material selected from the group consisting of cokeand flux is spread on the top of the starting material in the vessel.One or more flames of hydrocarbon fuel-oxygen mixture are directed tothe particulate layer, while translating the vessel along a closed path,so as to heat the particulate to white-hot state and to mix the coldstarting material with the particulate thus heated, for melting thestarting material. A composition-control agent is added in the materialthus melted for producing desired composition of molten metal, whilemaintaining the flames and the translation. A fluid curtain is formedaround the flames to inhibit the flames from directly burning the innersurface of the vessel.

14 Claims, 7 Drawing Figures Patented April 4, 1972 I 7 Sheets-Sheet lINVENTOR yaw? JM ATTORNEYS 7 Sheets-Sheet 2 Patented April 4, 1972 Fig.2

INVENTOR fiyasuA f 4044 ATTORNEYS Patented April 4, 1972 7 Sheets-Sheet5 a 3 1 m 5. 3 2 4 n 9 0 ()8 0. 2 5 I 7///////////// 6 /F\\ a 3 INVENTORATTORNEYS Patented A ril 4, 1972 7 Sheets-Sheet 4 INVENTOR fkasu f f/VJA ATTORNEYS Patented April 4, 1972 7 Sheets-Sheet 5 Fig.5

IN VENTOR yaw/K5 04 Y PJM ATTORNEYS Patented A ril 4, 1972 3,653,877

7 Sheets-Sheet 6 INVENTOR BY PJM ATTORNEYS METHOD OF MAKING MOLTEN METALFOR CASTING This invention relates to a method of making molten metalfor casting, directly from cold starting material. More particularly,the present invention relates to a method of making molten metal forcasting, directly from cold starting material, comprising steps ofplacing cold starting material in a vessel, covering the cold startingmaterial with a layer of particulate material selected from the groupconsisting of coke and flux, heating the particulate material layer byblowing one or more flames of hydrocarbon fuel-oxygen mixture into thevessel as separately delivered hydrocarbon fuel and oxygen are mixed,intermingling the heated flux and the cold starting material by rotatingthem in the vessel about an axis which is offset from the central axisof the vessel by translating the vessel along a closed path, adding acomposition-control agent in the molten metal being agitated by thetranslation, and producing a fluid curtain around the flames so as toinhibit the directly heating of the inner wall of the vessel by theflames.

According to a conventional method of making molten metal for molding,cold starting materials, such as cold pig iron, scrap iron, and variouschipped irons, are melted in a eupola, and then one or more additives,such as ferrosilicon and ferro-manganese, are added into the moltenmetal in the cupola through its tuyere in order to adjust thecomposition of molten metal so as to produce a desired composition. Themolten metal thus made in the cupola by the cupola by the conventionalmethod has various drawbacks: namely, that the contents of indispensableingredients of cast metal, e.g., silicon and manganese, are low; thatthe maximum amount of carbon to be added in the molten metal is limited,e.g., to about 3.5 percent in the case of iron; that a large amount ofgaseous elements, e.g., oxygen, hydrogen, nitrogen, etc., are dissolvedin the metal; that the sulfur content, which is critical to theproperties of cast metal, cannot be reduced. Accordingly, molten metalfor refined cast articles, such as molten iron for spheroidal graphitecast iron, which should be free from sulfur and oxygen, is furthertreated by transferring the molten metal from the cupola to an electricfurnace for refinement, e.g., desulfurization, carburization,deoxidation, etc. In order to avoid the transfer from the cupola to theelectric furnace, it has been also practised to melt solid metal in anelectric furnace to begin with, so that the melting and the refinementof the metal can be made continuously in the same electric furnace.

In any of the aforesaid conventional methods, the preparation of moltenmetal for refined cast metal articles requires the use of an electricfurnace. The electric furnace for the refining should be of closed type,in order to prevent the oxidation of the molten metal. Accordingly, theequipment for making the molten metal for refined cast articles areusually costly. In other words, an apparatus for making refined moltenmetal becomes economically feasible only when a large amount of suchrefined molten metal is necessary, but the use of the apparatus cannotbe economically justified for producing a small amount of the refinedmolten metal.

In order to make both the ordinary grade molten metal and the refinedmolten metal on a small scale, it has been a practice to melt coldstarting material in a cupola and to refine the composition of themolten metal in a ladle to which the molten metal is scooped. Accordingto a known refining method, one or more composition-control agents areadded into the molten metal in the ladle. At the same time, the moltenmetal is agitated by eccentrically rotating it at a high speed in theladle, to accelerate the reaction of the agents with the molten metal.With such combination of a cupola and a ladle, molten metals withdifferent degree of refinement can comparatively easily be made on asmall scale for a wide range of refinement. The eccentric rotation ofthe molten metal results in its quick reactions with the added agentsand an improvement of its venting quality. The combination of a cupolaand a ladle, however, has the following drawbacks.

1. In transferring the molten metal from the cupola into the ladle, themolten metal is cooled, even if the ladle is preheated. When the moltenmetal in the ladle is cooled to a temperature below a certain value, thecomposition refinement cannot be carried out effectively. To demonstratethe effects of the temperature of the molten metal on its refinement,the inventor has made a series of tests. Refining agents, orcomposition-controlling agents, which consisted of 2.5 percent of cokepowder, 10 percent of ferrosilicon, 0.3 percent of calcium-silicon, and1.5 percent of calcium carbide, were added into five samples of molteniron, which were previously transferred into different ladles from acupola. The molten metals were treated by eccentric rotation atdifferent temperatures. Measurement was made on the degree ofdesulfurization, and the yields of carbon and silicon, on the samplesthus treated. The results are shown in Table 1.

As shown in Table l, the inventor has confirmed that the success of thecomposition control of molten iron in a ladle largely depends on thetreating temperature thereof, more particularly the temperature of themolten iron in the ladle during the treatment.

Furthermore, the inventor made a test by measuring the temperaturechange in a process of scooping molten metal from a cupola into apreheated ladle for eccentric rotation. It was found that a temperaturedrop of 100C or more was inevitable in the scooping.

In short, with a cupola, it is usually difficult to raise thetemperature of molten metal to l,500 C. or higher, and the molten metaltemperature is dropped by 50 C. to 100 C. in transferring it into apreheated ladle. The eccentric rotation of the ladle and the addition ofthe compositioncontrol agents also cause heat loss from the molten metalin the ladle, resulting in a temperature drop of 50 C. to C. in suchrefining process.

(2) In the known method of making molten metal casting,

the refining is carried out only in a ladle, while using a cupola onlyfor melting. Accordingly, gaseous materials contained in the moltenmetal in the cupola, e.g., oxygen, hydrogen, nitrogen, are dispersed invain and cannot be used effectively for the refining purpose. Forinstance, the aforesaid gaseous materials have desulfurizing power, butsuch power cannot be used in a useful manner.

3. The known method comprises two steps, a cupola step and a ladle step,using two different equipments. Accordingly, the method is complicatedand time-consummg.

As pointed out in the foregoing, different methods of making moltenmetal for casting have been used depending on the kind and the amount ofthe metal to be case, but none of the conventional methods can get ridof the aforesaid shortcomings.

In order to obviate such shortcomings of the known methods, the inventorhas made a series of studies on a method and a device for selectivelymaking different kinds of molten metals for casting, by a simpleprocess, regardless of the amount of the molten metal required. As aresult, the inventor has succeeded in providing an improved method and adevice for making different kinds of molten metals, yet retaining allthe advantages of conventional methods.

The inventor noticed the following points.

a. Neutral flames of gaseous mixture of hydrocarbon-oxygen system, whichare commonly used in gas-welding, can heat the metal being welded to3,000 C. or higher, while the existence of welding flux materials (e.g.,borax, sodium silicate, etc.) substantially prevents oxidation of usefulelements in the metal being welded, such as carbon, silicon, andmanganese, during the welding. If such flames can be applied to themaking of molten metal for casting, the temperature of the molten metalcan be raised to a level considerably higher than that obtainable by acupola.

b. If both the melting step of the starting cold material and therefining step of the molten metal for casting can continuously be donein a common container, the aforesaid temperature drop of the moltenmetal during its transfer, from a cupola to a ladle, can be eliminated,together with the tedious preheating of the ladle.

c. In controlling the composition 'of the molten metal for casting, ifthe molten metal is heated while eccentrically rotating the molten metalin a container, e.g., a ladle, the molten metal can be thoroughly mixedwith compositioncontrol agents without causing any temperature drop ofthe molten metal. Thus, composition control, especially desulfurization,can quickly be effected.

In order to take advantage of the last mentioned points, the

inventor had to solve the following difficulties.

i. There is no readily available refractory lining material, whichwithstands a high temperature of 3,000 C. or higher, generated by flamesof the gaseous mixture of hydrocarbon-oxygen system. It is alsodifficult to melt cold starting material without causing oxidationthereof.

ii. Conventional welding burners for hydrocarbon-oxygen mixture are notsuitable for burning a large amount of gaseous fuel mixture.

After years of studies, the inventor has devised the followingcountermeasures to the above difficulties.

A. By preheating particulate material selected from the group consistingof coke and flux to a white-hot temperature and by thoroughly mixingcold starting material with the white-hot particulate material, the coldstarting material can be melted substantially instantly without causingany noticeable oxidation of the starting material.

B. In the case of making molten iron for casting, by burning a gaseousfuel mixture, e.g., that of hydrocarbon-oxygen system, while completelysurrounding the flame of the gaseous fuel mixture with a water curtain,the following special effects can be achieved.

a. The starting material can be heated by the flame of the gaseous fuelmixture to 3,000 C. or higher, without exposing the inner surface of acontainer of the starting material to such high temperature.

b. The existence of a water curtain results in generation of (CO+H gas,which tends to accelerate chemical reduction in the container.

c. The hydrogen thus generated permeates in the molten iron, so that theviscosity and the density of the gaseous materials dissolved in themolten iron are reduced. Accordingly, the venting quality andpermeability of the molten metal for casting are improved.

C. In the case of making molten nonferrous metal for easting, bycompletely surrounding one or more flames of hydrocarbon fuel-oxygenmixture, e.g., heavy-oil-oxygen mixture, with an air curtain, the innersurface of a vessel, containing such molten nonferrous metal, can beprotected from the high temperature of such flames.

D. By separately delivering hydrocarbon fuel and oxygenrich gas into thespace surrounded by the water curtain, and by mixing the hydrocarbonfuel and the oxygen-rich gas therein, it becomes possible to eliminatethe danger of backfire, or reverse flow of the hydrocarbon fuel oxygenmixture, which may lead to a large explosion. Thus, a large amount ofgaseous fuel mixture can effectively be burnt.

An object of the present invention is to provide a method for makingmolten metal for casting, which essentially comprises four differentprocesses; namely a first process of placing starting cold material in arefining vessel and then placing a of a particulate material selectedfrom the group consisting of coke and flux layer on the cold startingmaterial; a second process of heating the particulate layer to white-hotcondition by directing one or more flames of hydrocarbon fuel-oxygenmixture thereto from above the particulate layer; a third process ofmelting said cold starting material by continuing said injection of theflames of the hydrocarbon fuel oxygen mixture from above the vessel,while eccentrically rotating and agitating said cold starting materialand said white-hot particulate material in the. vessel by translatingsaid vessel along a closed locus; and a fourth process of continuingsaid injection of the flames, forming a water curtain so as to surroundthe flames, and adding composition-control agents into the molten metal,whereby a molten metal for casting with a desired composition isproduced.

For a better understanding of the invention, reference is made to theaccompanying drawings, in which:

FIG. 1 is an elevation, with a part in section, of a device forpracticing the method for making molten metal for casting, according tothe present invention;

FIG. 2 is a plan view of the device of FIG. 1;

FIG. 3 is a partial sectional view of an injector usable in the deviceof FIG. 1;

FIG. 4 is a sectional view, taken along the line IV-IV of FIG. 3;

FIG. 5 is a view similar to FIG. 1, illustrating a different embodimentof the present invention;

FIG. 6 is a sectional view, taken along the line VI-VI of FIG. 5; and

FIG. 7 is a vertical sectional view of a supporting cylinder of aframework in an embodiment of the present invention, which supportcylinder is suitable for alternately translating the framework along aclosed path in opposite directions.

Like parts are designated by like numerals and symbols throughout thedrawings.

Referring to FIGS. 1 to 4, a device for making molten metal for casting,embodying for practicing the method of the present invention, generallycomprises a vessel 1 for melting cold starting material and controllingthe composition of the molten metal by adding a composition-controlagent, an agitator 2 for translating the vessel 1 along a closed path soas to cause the molten metal in the vessel to swirl eccentricallytherein, and an injector 3 for injecting hydrocarbon fuel-oxygen mixturetoward the starting cold metal in the vessel 1 and for injecting a watercurtain surrounding the injected flame of the hydrocarbon fuel-oxygenmixture.

The vessel 1 can be a ladle of conventional construction. The lining ofthe vessel is not directly exposed to the high temperature of the flameof the fuel-gas-oxygen mixture, as will be described hereinafter.Accordingly, the inner surface of the vessel 1 can be lined withcomparatively inexpensive refractory material, such as chamotte.

The agitator 2 includes a substantially rectangular framework 4, whichintegrally supports the vessel 1 by means of clamps 13. In theillustrated embodiment, the four corners of the framework 4 are movablysupported by a suitable means on a stationary base 6 in such manner thatthe framework 4 can be translated along a closed circular path. Moreparticularly, four support cylinders 5a to 5d (to be collectivelyreferred to as 5) are secured to the base 6,and each of the supportcylinders 5a to 5d holds a rotary member 7a, 7b, 7c, or 7d (to becollectively referred to as 7"), respectively, which is rotatably fittedin the support cylinder. In order to facilitate the rotation of therotary member 7 in the cylinder 5, bearing balls 8 are inserted betweenthe bottom surface of the rotary member 7 and the inner bottom surfaceof the cylinder 5. Each rotary member 7 is provided with an eccentricshaft 9a, 9b, 90, or 9d (to be collectively referred to as 9), whichextends upwards from the top of the rotary member 7. The four supportcylinders 5 are so disposed on the base 6 that the four eccentric shafts9, each being carried by one of the support cylinders 5, can beconnected to the four corners of the framework 4, as can best be seenfrom FIG. 2.

To drive the translation of the framework 4, one of the rotary members,e.g., 7a, is driven by a motor 12 through a suitable transmission, forinstance the combination of a bevel gear secured to that rotary member7a and a bevel gear 11 secured to the output shaft of the motor 12. Whenthe rotary member 7a is driven by the motor 12, the rotary member 7arotates in the support cylinder 50 about the axis of the member 7a, sothat the eccentric shaft 9a secured to the rotary member 7a is rotatedabout the axis of the rotary member 7a. In other words, the eccentricshaft 9a rotates eccentrically, with respect to its own axis. Inresponse to the rotation of the eccentric shaft 9a, the rectangularframework 4 translates along a circular path, because the remainingrotary members 7b, 7c, and 7d follow the rotation of the rotary member70, while eccentrically turning the eccentric shafts 9b, 9c, and 9 dalong the identical paths with that of the eccentric shaft 7a atdifferent locations.

As a result of it, the vessel 1 carried by the framework 4 makes acircular translation together with the framework 4.

For simplicitys sake, the agitator 2 is illustrated as a means fortranslating the vessel 1 along a circular path, but the path of thetranslation is not limited to such a circle. For instance, by usingsuitable cam means instead of the eccentric shafts 9 of FIG. 1, thevessel 1 can be translated along a closed path of desired configuration,such as an elliptic path.

Similarly, the number of the support cylinders 5 and the rotary members7 is not limited to four, respectively, as illustrated in FIGS. 1 and 2.In fact, the vessel I can be movably supported by one support cylinder5, or by any suitable number of support cylinders 5, by slightlymodifying the structure of the framework 4 or the bottom of the vesselI, in a manner known to those skilled in the art.

In order to effect thorough stirring of the vessel 1, it is desirable totranslate the vessel 1 alternately in opposite directions, by a suitablemeans, such as a reversible motor, which may replace the motor 12 ofFIG. 1. When the direction of the translation of the vessel 1 isperiodically changed, a braking means must be used to bring the vesselquickly to rest. Due to the heavy weight of the vessel and the materialsloaded therein, a considerably long period of time elapses before thevessel comes to rest after the driving means, e.g., the motor 12, isde-energized. Thus, the overall efficiency of the melting device isreduced.

According to a feature of the present invention, there is provided ameans for quickly braking the movement of the vessel 1 at the time ofthe direction reversal of its translation. FIG. 7 illustrates theconstruction of supporting means which causes a vessel 1 to quickly stopafter the de-energization of a prime mover. In the figure, thesupporting means comprises a supporting cylinder 5 firmly secured to thebase 6 ofa metal-melting device. A rotary member 7 rotatably fits in thecylinder 5 in a concentric manner. Ball bearings'8 are inserted betweenthe lower surface of a contact plate 38 disposed at the bottom of therotary member 7 and the upper surface of the bottom wall of the supportcylinder 5, so as to ensure the smooth rotation of the member 7 relativeto the support cylinder 5. A cylindrical lower boss 34 is secured to therotary member 7 by a bolt 33, for receiving an eccentric shaft 9therein. The axis 8-8 of the eccentric shaft 9 is offset from the axisAA of the support cylinder 5, as shown in FIG. 7, by a given distanceD,. Roller bearings 35 are inserted between the eccentric shaft 9 andthe lower boss 34, for allowing smooth rotation of the eccentric shaft 9relative to the lower boss 34. In other words, the eccentric shaft 9 ofthis embodiment not only rotates about the axis AA of the supportcylinder 5 in an eccentric manner, but also spins about its own axisB-B. A cover 39 is provided at the top of the lower boss 34 to protectthe roller bearings 35 from dust particles. An upper boss 36 is securedto the lower surface of a framework 4 at such locations that the lowerends of the upper boss 36 operatively engages the upper end of theeccentric shaft 9. As a result, the eccentric rotation of the shaft 9causes the framework 4 to translate along a circular path, as describedhereinbefore, referring to FIGS. 1 and 2.

To provide for the improvement of the braking power, the supportingmeans of FIG. 7 includes a gap D between the outer peripheral surface ofthe top portion of the rotary member 7 and the inner peripheral surfaceof a top ring 32, which is secured to the top of the support cylinder 5by means of bolts 37. Another gap D is provided between the outerperipheral surface of the eccentric cylinder 9 and the inner peripheralsurface 36a of a vertically extending flange portion of the upper boss36.

When four supporting means, as shown in FIG. 7, are used in the agitator2 of FIGS. 1 and 2, the translation of the framework 4 and accordinglythe vessel 1 can be effected by connecting one of such supporting meansto the reversible motor 12 (not shown in FIG. 7) through a gear train.With the supporting means of FIG. 7, when the motor is de-energized, theframework 4 carrying the vessel I quickly comes to rest, as comparedwith the supporting means of- FIGS. 1 and 2. The two kinds of gaps D andD of Fig. 7 act to absorb or facilitate the absorption of the kineticenergy of the rotating framework 4 and the vessel 1, because thepresence of the gaps D and D causes the framework 4 to make irregularmovement due to the playing in the movement by the eccentric shaft 9 andthe rotary member 5. Without such gaps D and D;,, the vessel continuesits smooth movement for some time by inertia. The different supportingmeans of FIG. 7 may tend to move in different directions, so as toincrease the friction between adjacent moving parts and the brakingeffects of such means. As the time from the de-energization of the primemover, e.g., the reversible motor, of the melting device to the rest ofthe vessel decreases, the overall efficiency of the stirring operationof the contents of the vessel is improved, because the direction of thetranslation of the vessel can be changed more frequently in a givenperiod of time.

Referring to FIGS. 3 and 4, the injector 3 comprises concentricallydisposed cylindrical passages; namely, a central fuel passage 14 fordelivering fuel, such as acetylene, oxygen passage 15 for deliveringoxygen-rich gas, such as oxygen gas or air, a second fuel passage 14 fordelivering the same fuel as the central passage, cooling water passages16 for circulating cooling water by feeding cold cooling water throughone of the passages 16 while returning the warmed water through theother one of the passages 16, and a surrounding water passage 17 fordelivering water for producing water curtain, A mixing chamber 18 isformed at the lower end of the injector 3, which directly communicateswith the central hydrocarbon passage 14 through a throttle 19 forgasifying the fuel. The very lower ends of the oxygen passage 15 and thesecond fuel passage 14 are closed, and openings 20 and 21 are bored inthe proximity of the lower ends of those passages, respectively, so asto inject the oxygen-rich gas and gasified fuel into the mixing chamber18.

In other words, the oxygen passage 15 and the fuel passages 14, 14' areso disposed that the fuel and the oxygen are delivered separatelythrough the injector 3, until they are injected into the common mixingchamber 18. With such separate delivery of the fuel and oxygen, thedanger of back tire and ensuing explosion can completely be eliminated,which have been rather frequently encountered within conventionalacetylene gas burners.

Water curtain noules 22 are provided at the lower end of the surroundingwater passage 17, so as to direct a water curtain 27 in a directionobliquely away from the axis of the injector 3, while surrounding aflame 26 of the hydrocarbon fuel oxygen mixture thus mixed at the mixingchamber 18. By the use of the water curtain 27, the inner wall of thevessel 1 is protected from being directly heated by the flame 26 of thefuel mixture.

An end plate 3a of the injector 3 is exposed to the flame 26 of thehydrocarbon fuel oxygen mixture, but it can be made of common metallicmaterial, because it is cooled by water flowing through the coolingwater passages 16.

In operation, cold starting material 23, such as cold pig iron and scrapiron, is placed in the vessel 1. It is preferable to use granularmaterial 23, although bulky blocks of the cold starting material can bealso melted by the illustrated device of the invention. In the case ofthe bulky blocks of starting material 23, in order to improve itsmobility, finely chipped metal 24 is added in the vessel 1 forsurrounding the bulky blocks 23. It is also possible, and preferable, toform the cold starting material 23 with the chipped metal 24 alone. Thebulky blocks and the chipped metal will be referred to as cold startingmaterials 23, 24, because they are mixed together in the course ofmelting by translating the vessel 1 along a circular path.

The cold starting material 23 and the chipped metal 24 in the vessel 1are covered with a layer of coke powder 25, and the coke powder is thenheated to white-hot condition by the flame 26 of the hydrocarbonfuel-oxygen mixture from the injector 3. The white-hot coke powder thusheated acts as a heating medium in the course of melting the startingmaterials 23, 24. At the same time, the coke powder layer 25 preventsoxidation of the starting material 23, 24. Accordingly, in the processof heating the coke layer 25, no water curtain is necessary to surroundthe flame 26.

After coke layer 25 is made white-hot, the driving motor 12 is actuatedto drive the framework 4 along a circular path, together with the vessel1, as described in the foregoing. The inventor has foundthroughexperiments that in response to such translation of the vessel 1,the cold starting materials 23, 24 and the white-hot coke layer 25 beginto rotate about an axis, which is offset from the central axis of thevessel 1, whereby the white-hot coke is thoroughly mixed with thestarting materials 23, 24. The heat carried by the white-hot coke 25 istransferred to the starting materials 23, 24 to heat the latter. Thestarting materials 23, 24 are further heated by the flame 26 of thefuel-gas-oxygen mixture. The cold starting materials 23, 24 are thusmelted, to produce molten metal.

The hydrocarbon fuel to be used in the melting process is, for instance,acetylene, propane, or other similar combustible hydrocarbon gas. Withthe flame 26 made by burning such hydrocarbon fuel, the temperature ofthe starting materials 23, 24 is substantially instantly increasedwithout allowing oxidation of the material.

There is a known process of melting metal by blowing oxygen to themetal. The oxygen, however, consumes certain ingredients of the metalbeing melted, such as manganese, carbon, silicon, etc., and theoxidizing temperature of such ingredients is used for melting the metal.In casting iron or other metals, the aforesaid ingredients are necessaryto achieve satisfactory properties of the cast articles. Accordingly,the oxygen gas blowing process cannot be used for preparing molten metalfor casting.

The inventor has noticed the fact that acetylene-oxygen neutral flame isused in gas welding for achieving a temperature of 3,000 C. or higher,and he has found that other hydrocarbon fuel-oxygen flames can be usedfor melting cold starting material for the purpose of making moltenmetal for casting. For making molten iron, for casting, hydrocarbon,e.g., acetylene, is found to be preferable. In the case of gas weldingof metal, flux materials, such as borax and sodium silicate, are used inorder to separate oxides of the metal being welded as slags and toprevent ingredients in the metal, such as carbon, silicon, andmanganese, from being oxidized. The coke layer 25 in the vessel '1, asillustrated in FIG. 1, fulfills similar functions to those of fluxmaterials in gas welding. In other words, the whitehot coke powder 25acts not only as the heat carrying medium, but also as a medium forpreventing the metal being melted from oxidation and for preventingoxidation of various elements added to the metal being melted.

After the starting materials 23, 24 are melted, valves (not shown) ofthe water curtain nozzles 22 of the surrounding water passage 17 areopened, so as to produce a water curtain 27 surrounding the flame 26.With the water curtain 27, the inner surface of the vessel 1 isprotected from the flame 26. Furthermore, hydrogen gas H is generated atthe boundary between the flame 26 and the water curtain 27, by thermalcracking of water in contact with the flame 26.

The hydrogen gas H favorably behaves in various ways. Since hydrogen hasa large diffusion coefficient, it diffuses into the molten metal andaccelerates chemical reduction in the molten metal together with carbonmonoxide (CO) gas dissolved in the molten metal. The large heatconductivity of hydrogen, which is seven to ten times that of carbonmonoxide gas, improves heat conduction to the molten metal. It should benoted that the existence of hydrogen gas in the molten metal reduces theviscosity and density of gases dissolved in the molten metal, so thatits venting quality is improved. Thus, the danger of producing defectivecast articles is completely eliminated.

The presence of hydrogen gas in the vessel 1 also enables directpreparation of molten metal for casting from powdered ore, e.g.,magnetite sand, sintered ore, iron ore, or pelleted ore, becausehydrogen reduces the ore to separate the desired metal.

A suitable composition-control agent is added into the metal thusmelted, for adjusting its composition, depending on the desired kind ofthe cast good, such as common cast iron, or high grade cast iron.Typical agents for common cast iron or gray pig iron are, for instance,coke breeze, ferrosilicon, calcium silicon, etc.

Upon completion of the composition-adjustment, the molten metal becomesready for casting.

It is one of the important features of the invention that both themelting of a metal and the adjusting of its composition for readying itto casting are carried out continuously in one vessel withouttransferring the molten metal to any other container.

The present invention has been described by mostly referring to anexample of melting iron, but the invention is not restricted to iron,but it can be used for melting other metals, such as for preparingmolten metal of non-ferrous alloy for casting.

Only one injector 3 is shown in the embodiment of FIGS. 1 to 4, but thenumber of the injectors is not restricted to one. In fact, a pluralityof such injectors can be used for melting a comparatively large quantityof the cold starting material.

FIGS. 5 and 6 illustrate another embodiment of the invention, whichincludes three injectors 3 disposed at vertices of an equilateraltriangle, in symmetry with each other relative to the axis of avessel 1. Referring to FIG. 6, the three injectors 3 are secured towalls 28 of a belt-like triangular water tank 29 at the inside of threevertices thereof, respectively. A surrounding water passage 17 isconnected to the top of the water tank 29, while a plurality of watercurtain nozzles 22 are bored on the bottom wall of the water tank 29.Accordingly, three flames 26 of fuel-gas-oxygen mixture from the threeinjectors 3 are enclosed by a triangular water curtain 27 from the watertank 29.

In the embodiment of FIGS. 5 and 6, it is not necessary to use thesurrounding water passage in each injector 3. The single surroundingwater passage 17 connected to the water tank 29, as shown in FIG. 5,will be sufficient.

While a large amount of cold starting materials 23, 24 is placed in thevessel 1, the agitator 2, especially the framework 4 thereof, is exposedto a very heavy load. The support cylinders 5 are subjected to a heavythrust load. In order to diversify the heavy thrust load, a plurality ofpneumatic bearing balls 31 are disposed between the base 6 and aheat-insulating plate 30, which is secured to the bottom of the vessel1.

Each of the pneumatic bearing balls 31 is made of about 5 mm thickrubber shell. In a preferred embodiment, the ball consists of threerubber layers; namely, an outer rubber layer with high resistances toaging, bending, and fatigue; an intermediate layer which withstands ahigh internal pressure of the ball; and an inner layer with highairtightness.

The pneumatic bearing ball 31, for instance, can withstand an internalpressure of about Kglcm or can bear a load of 10 tons or more per ball.

The translation of the vessel 1, by means of the agitator 2, eliminatesuneven distribution of the load, because the translation aims at evendistribution of the cold starting material and the homogeneous mixtureof the molten metal with the composition-control agent. In short, themechanical load on the framework 4 and the support cylinder 5 are welldiversified, so that smooth translation of the vessel 1 can be ensured.

The invention will now be described in further detail, referring toexamples.

EXAMPLE I Cold starting material consisting of 100 Kg of chipped ironand 400 Kg of scrap steel was placed in a vessel 1, as shown in FIG. 1.Table 2 shows the compositions of the chipped iron and the scrap steel.The cold starting material was covered by a coke layer by spraying 45 Kgof coke with composition, as shown in Table 3, on the surface of thestarting metal.

A hydrocarbon fuel-oxygen mixture was prepared by using acetylene as thehydrocarbon, in which the partial pressure of oxygen was about 3 Kg/cm,while the partial pressure of acetylene was about 0.4 Kg/cm. The cokelayer was heated to white-hot by burning the gaseous mixture. A drivingmotor 12 was then actuated to agitate the vessel ll, while maintainingthe burning flame 26 of the gaseous mixture, so that the starting metaland the coke layer rotated in an eccentric manner relative to the axisof the vessel.

It was confirmed by observation that as the coke got mixed with the coldstarting material, the material began to melt. The temperature of theflame 26 was raised by increasing the partial pressure of acetylene toabout 1 Kg/cm. At the same time a valve on a surrounding water passage17 was opened to form a water curtain 27. The rate of water supply tothe water curtain 27 was so controlled that water vapor of l,000 C. orhigher was generated in the proximity of the molten metal thus prepared.The average temperature of the molten metal in the vessel 1 increased toabout l,000 C. in about 5 minutes after forming the water curtain 27.

Then, Wt percent of coke, based on the total weight of the startingmetal, 1.05 Wt percent of ferrosilicon, and 0.35 Wt percent of calciumsilicon were added into the molten iron, while continuing the agitationof the vessel 1. Tables 3, 4, and 5 show the composition of the coke,ferrosilicon, and calcium silicon thus added, respectively.

TABLE 4 Ingredients of ferro- Silicon Carbon Phosphorus Sulfur siliconless than less than less than Percentage 75-78 0.3 0.05 0.05

TABLE 5 Ingredients of calcium Calcium Silicon Carbon silicon Percentage30-35 55-65 Less than When the temperature of the molten metal in thevessel 1 reached about 1,500 C., valves for all the passages of theinjector 3 are closed, to cease the formation of the flame 26 and thewater curtain 27. The agitation of the vessel 1 lasted for 3 minutesafter the ceasing of the flame, and then the agitator 2 was stopped.

After removing the slag layer floating on the molten iron, gray pig ironwas produced by casting the molten iron. Table 6 shows the compositionof the gray pig iron thus produced. As can be seen from the table, thegray pig iron had excellent mechanical strength.

TABLE 6 Ingredients of gray pig iron, Percentage: Carbon 3.75; silicon,1.56; Manganese, 0.48; Phos horns, 0.089; sulfur, 0.091; Tensilestrength (kg. mm. 22.2; Hardness (HB), 190.

In this example, the amount of oxygen used was about 1,400 liters, andthat of acetylene was about 400 liters, which amounts were about 20percent less than the corresponding amounts required in conventionalmethods.

Thus, the method of the present invention reduces the fuel cost ofpreparation of molten metal for casting.

EXAMPLE 2 Cold starting material consisting of 500 Kg of magnetite sandwas placed in a vessel 1, as shown in FIG. 1, and the surface of themagnetite sand was covered by spreading thereon 50 Kg of coke and 10 Kgof lime or calcium oxide. Table 7 shows the composition of the magnetitesand used in this example.

An acetylene-oxygen mixture, in which the partial pressure of oxygen wasabout 3 Kg/cm and that of acetylene was about 0.4 Kglcm was burned toproduce a flame 26 for heating the coke to white-hot temperature. Thewhite-hot coke was then mixed with the magnetite sand by agitating thevessel 1 while maintaining the flame 26, in the same manner asExample 1. Thus, the magnetite sand was melted.

Then the temperature of the flame 26 was raised by controlling thepartial pressure of oxygen at about 5 Kg/cm and the partial pressure ofacetylene at about 1 Kg/cm. At the same time, a water curtain 27 wasformed in such manner that the temperature of steam at the surface ofthe molten iron was l,000 C. or higher. The molten iron started to boilin about 8 minutes after the formation of the water curtain 27. Then,the flame 26 and the water curtain 27 were ceased for about 2 minutes,while holding the vessel 1 stationary. After removing the slag layerfloating on the molten iron, a steel sample was made by casting themolten iron. Table 8 shows the composition of the steel sample thusproduced.

TABLE 8 Ingredients of cast steel, Percentage: Carbon, 0.03; silicon,Manganese, 0; Phosphorus, 0.05; sulfur, 0.91,

Thus, it has been confirmed that molten steel can be made continuouslyand directly from magnetite sand, by taking advantage of the presence ofthe water curtain. Furthermore, it has been demonstrated that bycontrolling the carbon content, molten metal for casting can directly beobtained from granular ore, or in this case molten iron from magnetitesand. The amounts of oxygen and acetylene used in this Example wereabout 2,000 liters and about 600 liters, respectively.

EXAMPLE 3 A nonferrous cold starting material, consisting of copper,bronze, tin, and zinc at ratios as shown in Table 9 was placed in avessel 1, as depicted in FIG. 1. Neutral flux consisting of 5 Kg ofborax and 5 Kg of scrap glass were spread on the surface of thenonferrous metal, so as to cover the latter.

TABLE 9 Ingredients of nonferrous starting material, Weight (Kg.):Bronze blocks, 400; Copper wire scrap, 88; Tin blocks, 10; Zinc blocks,2; Total, R

A hydrocarbon fuel-oxygen mixture, consisting of heavy oil and air, inwhich the oxygen content was enriched by percent to an oxygen partialpressure of about 2 Kg/cm was injected into the vessel 1 through aninjector 3, to generate a flame 26 for melting the neutral flux. Table10 shows various properties of the heavy oil used.

TABLE 10 (Properties of heavy oil used in Example 3) Item Value Specificgravity 0. 94 Flash point, C 111 Bom degree 16-24 Carbon residue,percent 5. 7

By agitating the vessel 1, the flux and the cold starting material weremixed, and the starting material began to melt. Then, the partialpressure of the air in the fuel-gas-oxygen mixture was raised to about 3Kglcm while enhancing the partial pressure of the heavy oil therein. Atthe same time, an.

air curtain was formed about the flame 26. The temperature of Porosity,percent .I I

the molten metal increased to about 1,150 C. in 20 minutes after theformation of the air curtain 27a. Then, the flame 26 and the air curtain27a were ceased, and 2.5 Kg of lime stone was added into the moltenmetal. The molten metal in the vessel l was forced to move in the vessel1 about an axis which is offset from the central axis of the vessel 1.The forced agitation lasted for about 5 minutes, to effect thoroughdegassing. Thus, a molten metal ready for casting was achieved, and asound bronze sample was cast by pouring the molten metal. Table 11 showsthe composition of the bronze sample thus prepared.

TABLE 1 l Melting method Known reduction Method melting of the Itemmethod invention Composition:

Copper 86. 88. 74 Th1 10.08 9. 89 Zinc 1.18 1. 24 Lead Iron Tensilestrength (kg/mm 27 34 Elongation, percent. 22 46 Specific gravity 8. 2748. 843 6. 98 0. 64

In order to demonstrate the features of the method according to thepresent invention, the same cold nonferrous starting material was meltedby a known reduction-melting method, in which the starting metal wasplaced in a rotary crucible, which was then heated in a reducingatmosphere by means of a heavy oil burner. Various properties of asample made by casting the molten metal thus produced are also shown in.Table l 1.

It is apparent from Table l 1 that the composition of the cast metal wasso improved by the present invention that the mechanical strength of themetal melted by the method of the invention is greater than that meltedby the known reductionmelting method.

Furthermore, the time necessary for melting the metal was considerablysaved, as comparedv with that of the known reduction-melting method,which requires about one hour. With the method of. the invention, oxygengas or oxygen-enriched air could be used in the hydrocarbon fuel-oxygenflame 26 without causing any adverse effect on the inner lining of thevessel 1.

The salient features of the method according to the present inventioncan be summarized as follows.

1. With the method of the invention, the cold starting material ismelted in a vessel, while simultaneously controlling the compositionthereof, in a very quick and simple manner. As a result, a high thermalefficiency can be achieved.

2. In the method of the present invention, the melting of the coldstarting material is carried out by using an intermediate coke layerspread on the surface of the metal. Accordingly, the metal issubstantially instantly melted without causing the metal to be oxidized.Furthermore, the composition of the metal can be controlled by using asuitable agent, while rotating the molten metal in the vessel about anaxis which is offset from the central axis of the vessel, and whileenclosing the molten metal with a water or air curtain. Thus, variousgaseous elements generated in the course of melting, such as oxygen,hydrogen, and nitrogen, can be utilized for the control of the metalcomposition. For instance, desulfurizing agents can be used veryeffectively in the method of the invention, because their desulfurizingpower can be supplemented with the action of gaseous substance generatedin the process of melting the metal, so as to produce a sound low-sulfurmolten iron for making spheroidal graphite cast iron.

3. It is an important feature of the invention that the control of thecomposition of the molten metal for casting can be carried out veryquickly, because the molten metal can be heated to a high temperature bythe combustion of hydrocarbon fueloxygen mixture. Thus, the effects ofcarburization and desulfurization can be improved.

4. With the method of the invention, large particles or blocks of thecold starting material and coke can be used, because such particles orblocks are forced to rotate in a vessel about an axis which is offsetfrom the central axis of the vessel. If a cupola is used for melting themetal, the grain size of the starting material must be limited within acertain range.

5. The use of an air or water curtain surrounding the flame offuel-gas-oxygen mixture protects the refractory lining of the vesselfrom direct heating by the flame. Accordingly, the lining can be madewith commonly used refractorymaterial, such as chamotte.

6. If a water curtain is used, hydrogen gas (H is generated at thecontact of the water curtain with the flame of the gaseous mixture. Thehydrogen gas thus generated accelerates the reducing reaction of themolten metal and reduces the viscosity of gases dissolved in the moltenmetal, so that the heat transfer through the molten metal can beimproved.

7. In the device of the invention, fuel-gas is delivered to the point ofejection through a separate passage from that of oxygen or air, so thatthe desired hydrocarbon fuel-oxygen mixture is formed only at a positionwhere the mixture is burnt, which position can be enclosed by the wateror air curtain. Thus, the danger of back fire is completely eliminated.With such arrangement, a large amount of the gaseous mixture-can beburnt effectively while ensuring the complete exclusion of the risk ofexplosion of the gaseous mixture. 8. The direction of the translation ofthe melting vessel can quickly be reversed simply by using a reversiblemotor, whereby the stirring effects of the contents of the vessel cangreatly be improved.

Iclaim:

l. A method of making molten metal for casting, comprising steps ofplacing cold starting material in a vessel and covering the top of thestarting material in the vessel with a layer of particulate materialselected from the group consisting of coke and flux, forming hydrocarbonfuel-oxygen mixture at a position immediately above the vessel in acontinuously cooled environment by mixing separately deliveredhydrocarbon fuel and oxygen-rich-gas; burning the hydrocarbonfuel-oxygen mixture as being formed, so as to blow a flame of thehydrocarbon fuel-oxygen mixture to said layer of particulate materialfor heating said layer of particulate material whitehot; translating thevessel substantially horizontally along a closed path so as to cause thestarting material and said particulate material in the vessel to rotatein the vessel about an axis which is offset from the central axis of thevessel, in order to force the white-hot flux to be mixed with thestarting material; melting the starting material by continuing saidtranslation of the vessel while maintaining said blowing of the flame;adding a composition-control agent in the molten material whileagitating the molten material for preparing composition of the metal forcasting; and producing a fluid curtain around the flame to inhibit theflame from directly heating the inner surface of the vessel, said fluidbeing selected depending on the kind of metal being melted.

2. A method according to claim 1, wherein said hydrocarbon fuel isethylene.

3. A method according to claim 1, wherein said vessel is translatedalong a circular path.

4. A method of making molten iron for casting, comprising steps ofplacing cold starting iron material in a vessel and covering the top ofthe iron material in the vessel with a coke powder layer; forminghydrocarbon fuel-oxygen mixture at a position immediately above thevessel in a continuously cooled environment by mixing separatelydelivered hydrocarbon fuel and oxygen-rich-gas; burning the hydrocarbonfueloxygen mixture as being formed, so as to blow a flame of thehydrocarbon fuel-oxygen mixture to the coke layer to heat the coke layerwhite-hot; translating the vessel substantially horizontally along aclosed path so as to force the cold iron material and the coke in thevessel to rotate in the vessel about an axis which is offset from thecentral axis of the vessel in order to force the white-hot coke to bemixed with the iron material; melting the iron material by continuingsaid translation of the vessel while maintaining said blowing of theflame;-

adding a composition-control agent in the molten iron material forpreparing a desired composition suitable for casting; and producing awater curtain around the flame to inhibit the flame from directlyheating inner surface of the vessel.

5. A method according to claim 4, wherein said continuously cooledenvironment is formed by circulating cooling water through a passagewhich surrounds passages for separately delivering the hydrocarbons fueland said oxygenrich-gas and surrounds a mixing portion of thehydrocarbon fuel and the oxygen-rich-gas.

6. A method according to claim 4, wherein said oxygenrich-gas is pureoxygen.

7. A method according to claim 4, wherein said cold starting ironmaterial is selected from the group consisting of chipped iron, scrapiron, pig iron, gray pig iron, and a mixture thereof.

8. A method according to claim 4, wherein said cold starting ironmaterial is selected from the group consisting of magnetite sand,sintered iron ore, powdered iron ore, and pelleted iron ore.

9. A method according to claim 4, wherein said composition-control agentis selected from the group consisting of coke breeze, silica, naturecoke, ferro-manganese, lime stone, fluorite, ferrosilicon, siliconmanganese, and a mixture thereof.

10. A method of making molten nonferrous metal for casting, comprisingsteps of placing cold nonferrous metal material in a ladle-like vesseland covering the top of the nonferrous metal material in the vessel witha flux layer; forming hydrocarbon fuel-oxygen mixture at a positionimmediately above the vessel in a continuously cooled environment bymixing separately delivered hydrocarbon fuel and oxygen-richgas; burningthe hydrocarbon fuel-oxygen mixture as being formed, so as to blow aflame of the hydrocarbon fuel-oxygen mixture to the flux layer to heatthe flux layer white-hot; translating the vessel substantiallyhorizontally along a closed path so as to force the cold nonferrousmetal material and the flux in the vessel to rotate in the vessel aboutan axis which is offset from the central axis of the vessel in order toforce the whitehot flux to be mixed with the nonferrous metal material;melting the nonferrous metal material by continuing said translation ofthe vessel while maintaining said blowing of the flame; adding acomposition-control agent in the molten nonferrous metal material forpreparing a desired composition suitable for casting; and producing anair curtain around the flame to inhibit the flame from directly heatinginner wall of the vessel.

11. A method according to claim 10, wherein said oxygenrich-gas is air.

12. A method according to claim 10, wherein said flux is selected fromthe group consisting of borax, glass, sodium silicate, and a mixturethereof.

13. A method according to claim 10, wherein said hydrocarbon fuel isheavy oil.

14. A method according to claim 10, wherein said composition-controlagent is selected from the group consisting of coke breeze, silica,nature coke, lime stone, fluorite, silicon manganese, and a mixturethereof.

2. A method according to claim 1, wherein said hydrocarbon fuel isethylene.
 3. A method according to claim 1, wherein said vessel istranslated along a circular path.
 4. A method of making molten iron forcasting, comprising steps of placing cold starting iron material in avessel and covering the top of the iron material in the vessel with acoke powder layer; forming hydrocarbon fuel-oxygen mixture at a positionimmediately above the vessel in a continuously cooled environment bymixing separately delivered hydrocarbon fuel and oxygen-rich-gas;burning the hydrocarbon fuel-oxygen mixture as being formed, so as toblow a flame of the hydrocarbon fuel-oxygen mixture to the coke layer toheat the coke layer white-hot; translating the vessel substantiallyhorizontally along a closed path so as to force the cold iron materialand the coke in the vessel to rotate in the vessel about an axis whichis offset from the central axis of the vessel in order to force thewhite-hot coke to be mixed with the iron material; melting the ironmaterial by continuing said translation of the vessel while maintainingsaid blowing of the flame; adding a composition-control agent in themolten iron material for preparing a desired composition suitable forcasting; and producing a water curtain around the flame to inhibit theflame from directly heating inner surface of the vessel.
 5. A methodaccording to claim 4, wherein said continuously cooled environment isformed by circulating cooling water through a passage which surroundspassages for separately delivering the hydrocarbons fuel and saidoxygen-rich-gas and surrounds a mixing portion of the hydrocarbon fueland the oxygen-rich-gas.
 6. A method according to claim 4, wherein saidoxygen-rich-gas is pure oxygen.
 7. A method according to claim 4,wherein said cold starting iron material is selected from the groupconsisting of chipped iron, scrap iron, pig iron, gray pig iron, and amixture thereof.
 8. A method according to claim 4, wherein said coldstarting iron material is selected from the group consisting ofmagnetite sand, sintered iron ore, powdered iron ore, and pelleted ironore.
 9. A method according to claim 4, wherein said composition-controlagent is selected from the group consisting of coke breeze, silica,nature coke, ferro-manganese, lime stone, fluorite, ferrosilicon,silicon manganese, and a mixture thereof.
 10. A method of making moltennonferrous metal for casting, comprising steps of placing coldnonferrous metal material in a ladle-like vessel and covering the top ofthe nonferrous metal material in the vessel with a flux layer; forminghydrocarbon fuel-oxygen mixture at a position immediately above thevessel in a continuously cooled environment by mixing separatelydelivered hydrocarbon fuel and oxygen-rich-gas; burning the hydrocarbonfuel-oxygen mixture as being formed, so as to blow a flame of thehydrocarbon fuel-oxygen mixture to the flux layer to heat the flux layerwhite-hot; translating the vessel substantially horizontally along aclosed path so as to force the cold nonferrous metal material and theflux in the vessel to rotate in the vessel about an axis which is offsetfrom the central axis of the vessel in order to force the white-hot fluxto be mixed with the nonferrous metal material; melting the nonferrousmetal material by continuing said translation of the vessel whilemaintaining said blowing of the flame; adding a composition-controlagent in the molten nonferrous metAl material for preparing a desiredcomposition suitable for casting; and producing an air curtain aroundthe flame to inhibit the flame from directly heating inner wall of thevessel.
 11. A method according to claim 10, wherein said oxygen-rich-gasis air.
 12. A method according to claim 10, wherein said flux isselected from the group consisting of borax, glass, sodium silicate, anda mixture thereof.
 13. A method according to claim 10, wherein saidhydrocarbon fuel is heavy oil.
 14. A method according to claim 10,wherein said composition-control agent is selected from the groupconsisting of coke breeze, silica, nature coke, lime stone, fluorite,silicon manganese, and a mixture thereof.